GSEB Class 7 Science Solutions Chapter 9 Soil

Tick the Most Suitable Answer in Questions 1 and 2

 

Question 1. In addition to the rock particles, the soil contains
(i) air and water
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants
Answer: (iii) minerals, organic matter, air and water
In simple words: Soil has small bits of rock, but it also contains important things like minerals, decomposed plant and animal parts, air, and water.

Exam Tip: Remember that soil is a complex mixture, not just crushed rock. Understanding its components is crucial for comprehending its properties.

 

Question 2. The water holding capacity is the highest in:
(i) sandy soil
(ii) clayey soil
Answer: (ii) clayey soil
In simple words: Clayey soil can hold the most water because it has very small particles that pack closely together, leaving tiny spaces that trap water.

Exam Tip: Associate particle size with water retention. Smaller particles mean more surface area to hold water, hence clayey soil excels at it.

 

Question 3. Match the items in Column I with those in Column II:

Answer:

Exam Tip: When matching, look for key characteristics. For example, the topsoil is rich in organic matter (humus) which makes it dark, while sandy soil is known for its large particles.

 

Question 4. Explain how soil is formed.
Answer: Soil formation is a long, gradual process involving several stages:

• Initially, large and heavy rocks are broken down into smaller pieces, eventually appearing on the Earth's surface.
• Soil is then formed as rocks are broken apart by natural forces like wind, water, and climate. This natural process is referred to as weathering.
• The smaller rock particles created by weathering continue to break down further when exposed to air and moisture for long periods.
• Finally, the decomposed parts of dead plants and animals become mixed with the soil that formed from these processes. This gives the soil important energy in the form of organic matter.

In simple words: Soil is made over a very long time. Big rocks slowly break into smaller pieces because of wind, water, and weather. These small pieces then mix with dead plants and animals, making the rich soil we see.

Exam Tip: Remember the two main components of soil formation: weathering of rocks and the addition of organic matter from plants and animals. Emphasize that it is a continuous, slow process.

 

Question 5. How is clayey soil useful for crops?
Answer: Clayey soil possesses an excellent capacity for retaining water. It is also full of humus and is exceptionally fertile. This is the main reason why this type of soil is beneficial for growing crops like wheat and rice.
In simple words: Clayey soil is good for crops because it holds a lot of water and has many nutrients from humus, which helps plants like wheat and rice grow well.

Exam Tip: Focus on the two main advantages of clayey soil for agriculture: high water retention and rich humus content, which both contribute to its fertility.

 

Question 6. List the differences between clayey soil and sandy soil.
Answer:
Clayey soil:

• The proportion of fine particles is greater than big particles.
• It has a lower percolation rate of water.
• It possesses a good water holding capacity.

Sandy soil:

• The proportion of big particles is greater than fine particles.
• It has a higher percolation rate of water.
• It has a poor water holding capacity.

Exam Tip: When comparing soil types, always mention particle size, water percolation rate, and water holding capacity as these are key distinguishing features.

 

Question 7. Sketch the cross section of soil and label the various layers.
Answer: A soil cross-section typically shows distinct layers, or horizons, which can be described as follows:
The uppermost layer, the A-horizon (Topsoil), is often divided into sub-layers like A\(_{0}\) (organic layer), A\(_{1}\), A\(_{2}\), and A\(_{3}\). This layer is rich in humus and vital for plant growth.
Below the A-horizon is the B-horizon (Subsoil), which may also have sub-layers like B\(_{1}\), B\(_{2}\), and B\(_{3}\). This layer contains less organic matter but accumulates minerals leached from the topsoil.
The deepest layer shown is the C-horizon (Substratum), which consists of partially weathered parent rock. Below this is the bedrock, the unweathered parent material.

Exam Tip: When describing soil horizons, name each major layer (A, B, C) and briefly mention its key characteristics, such as organic content, mineral accumulation, and weathering status.

 

Question 8. Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Answer:
Given that:
Amount of water \( = 200 \) mL
Time taken \( = 40 \) minutes
Rate of percolation (mL/min) \( = \frac{\text{amount of water}}{\text{percolation time}} \)
\( = \frac{200 \text{ mL}}{40 \text{ min}} \)
\( = 5 \text{ mL/min} \)
In simple words: To find out how fast water goes through soil, you just divide the amount of water that soaked in by the time it took. In this case, 200 milliliters divided by 40 minutes gives us 5 milliliters per minute.

Exam Tip: Always state the formula clearly before substituting values. Ensure units are consistent and included in your final answer for full marks.

 

Question 9. Explain how soil pollution and soil erosion could be prevented.
Answer:
Prevention of soil pollution:

• Waste products and chemicals should be properly treated before they are released into the soil.
• The use of pesticides should be minimized.
• There should be a ban on polythene bags and plastics.

Prevention of soil erosion:

• By planting more trees.
• By avoiding deforestation.
• By helping to maintain the porous structure of soil.
• Controlling and reclaiming ravines and stopping shifting cultivation.

Exam Tip: Categorize your prevention methods clearly for soil pollution and soil erosion. For pollution, think about reducing harmful inputs; for erosion, focus on maintaining soil cover and structure.

 

Question 10. Solve the following crossword puzzle

Across:
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.

Down:
1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.
Answer:

Exam Tip: For crossword puzzles, read both Across and Down clues carefully. Sometimes, an answer from one direction helps confirm letters for another.

Extended Learning - Activities And Projects

 

Question 1. Boojho would like to know the difference between raw and baked soil? Investigate how the soil from which matkas are made is different from the soil used to make statues.
Answer:
Raw soil: This is soil that has not been heated. It typically appears white or a dull blackish color. Raw soil contains water molecules within it and also has air present.
Baked soil: When raw soil is heated, it becomes known as baked soil. This heating process causes it to lose its water molecules, and its color changes to reddish. The soil used for making 'matkas' (earthen pots) is usually mixed with horse-dung and prepared before being baked. Statues, however, are generally formed from the best quality of raw clay soil.
In simple words: Raw soil is just natural soil with water and air. Baked soil is raw soil that has been heated, making it lose water and turn reddish. Matkas are made from mixed, baked soil, while statues use fine raw clay.

Exam Tip: Differentiate between raw and baked soil based on heat treatment, water content, and color change. Note the specific soil types and preparation methods for different crafts like matkas and statues.

 

Question 2. Paheli is worried. She could see a brick kiln from her house. Bricks were being made there. There was so much smoke coming out of the kiln. She was told that the best quality of clay is required for making pottery, statues and bricks. She has seen truck loads of bricks being taken away for construction of buildings. At this rate, she fears, no soil will be left. Are her fears justified? Discuss this problem with your parents, teachers and other experts of your area and prepare a report.
Answer: Paheli's fears are partially justified, but also somewhat incorrect. Soil does possess the natural ability to gradually replenish itself, so the fear that "no soil will be left" is not entirely accurate in the short term. However, if soil is used at a significantly higher rate than its natural replenishment rate, then her fear becomes justified. Excessive removal of topsoil for brick making, especially without proper replenishment or sustainable practices, can lead to long-term soil degradation and scarcity in certain areas. This problem should be discussed with parents, teachers, and local experts to understand the balance between resource use and environmental sustainability.
In simple words: Paheli's worry is partly right. Soil can grow back slowly, so it won't run out completely quickly. But if we keep taking too much soil too fast for making bricks, it can cause problems and harm the land over time.

Exam Tip: When addressing environmental concerns, consider both natural processes (like soil replenishment) and human impact (rate of resource extraction). A balanced answer acknowledges both the resilience of nature and the potential for human-induced harm.

 

Question 3. Try to find out the moisture content of a soil sample. One method is given here. Activity: Take 100 g soil. (Take help from any shopkeepers to weigh the soil.) Place it on a newspaper in the sun and allow it to dry for two hours. This activity is best done in the afternoon. Take care that the soil does not spill outside the newspaper. After drying it, weigh the soil again. The difference in the weight of the soil before and after drying gives you the amount of moisture contained in 100 g of soil. This is called the percentage moisture content. Suppose your sample of soil loses 10 g on drying. Then Per cent of moisture in soil \( = \frac { \text{wt. of moisture (g)} }{ \text{Original wt. of soil sample (g)} } \times 100 \) In this example: Per cent of moisture in soil \( = \frac { 10 \times 100 }{ 100 } = 10\% \)
Answer: To find the moisture content of a soil sample, you would follow the steps of the given activity. First, take a known amount of soil, for example, 100 grams, and record this as the initial weight. Next, spread the soil on a newspaper in the sun and allow it to dry completely, typically for a few hours, ensuring no soil is lost. After drying, weigh the soil again to get its final dry weight. The difference between the initial wet weight and the final dry weight represents the amount of water lost. To calculate the percentage of moisture, divide the weight of the lost water by the original wet weight of the soil and then multiply by 100. For instance, if 100g of soil loses 10g of water, the moisture content is 10%. By performing this activity with different soil samples, you can compare their respective moisture holding capacities.
In simple words: To find out how much water is in soil, weigh it when wet, then dry it completely and weigh it again. The weight difference is the water. Divide the water weight by the wet soil weight and multiply by 100 to get the percentage of moisture. You can do this for different soils to see which holds more water.

Exam Tip: When performing or describing experiments, always outline the procedure clearly, state the measurements taken, and show the calculation steps. Emphasize the importance of accurate initial and final weights.